An integrated starter-generator (ISG) serves as both a starter motor for an interncal combustion engine (ICE) and as an alternator. Thus, an ISG provides both additional torque to an engine when needed, and supplies electrical power to an electrical system of a vehicle. In automatic vehicle start-stop systems, ISGs are used for restarting the engine from a temporary stop.
ISGs may drive rotation of the engine via a mechanical coupling, such as a belt. Hydraulic belt tensioners are typically included to maintain the tension of the belt. During engine operation, a spring included in the hydraulic tensioner automatically increases belt tension whenever there is a loss in belt tension. However, during an engine start, the belt tension must be high enough for the ISG to provide the requisite starting torque to the engine. Thus, prior to commanding an engine stop, an engine controller may first ensure that the belt tension is sufficiently high such that the engine can be started during a subsequent engine start.
However, the inventors herein have recognized potential issues with such systems. As one example, when the engine stops unexpectedly, such as during an engine stall, the tensioner cannot be pre-emptively primed to the high tension mode. While the engine is off, belt tension cannot be increased because the spring force of the tensioner is alone not sufficient to increase belt tension. If the belt tension is too low to start the engine at the time of the engine stop, the engine may not restart.
In one example, the issues described above may be at least partially addressed by a method for tensioning a belt of a belt drive of an internal combustion engine not in operation and having a crankshaft, in addition to the belt as a traction means a first driving wheel arranged on the crankshaft and a third wheel arranged on a shaft of a starter assigned to the belt drive, wherein the belt is guided around the driving first wheel and the third wheel, and a movable tensioning means assigned to an active tensioner is provided, which engages in the belt under application of force by a spring, forming a contact zone, and applies tensile forces to the belt along its longitudinal axis for tensioning, comprising, controlling the active tensioner such that a compression of the spring is at least countered, so that a movement of the tensioning means under the load of the belt is at least hindered, and then exciting the belt to vibration in the contact zone by use of the starter so that the tensioning means, exposed to the force of the spring, is moved further in the direction of the belt under expansion of the spring, whereby the belt is tensioned. Thus, by vibrating the belt, the belt can be repeatedly relaxed and tightened to induce expansion of the tensioner spring and thus tightening of the belt.
In another example, a method for an engine system comprises, during an engine stop, pulsing a starter motor to relax a belt of a belt drive around a tensioner pulley of the belt drive and induce extension of a tensioner spring.
In another example, an engine system comprises a starter motor, and a controller with computer readable instructions stored in non-transitory memory for: prior to an engine start, varying an amount of power supplied to the starter motor to induce vibration of a belt of a belt drive of the engine system when a tension of the belt is less than a threshold.
In this way, belt tension during an engine stop may be increased, and therefore engine start failures may be reduced. In particular belt tension may be increased by vibrating the belt via torque oscillations of the starter motor, and inducing a tensioner spring to extend and push a tensioner pulley into the belt, thereby reducing the area enclosed by the belt (e.g., increasing the winding of the belt).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.